This invention relates to a pipe made of a rigid thermoplastic resin, a pipe joint structure, and manufacturing methods thereof, and more particularly to a pipe made of a rigid thermoplastic resin which is suitable as a pipe joint incorporating a sealing structure, a specific pipe joint structure, and their manufacturing methods.
A pipe joint, for example, an air-pressure joint usually secures a seal between an outer side (atmospheric air side) and an inner side (high pressure side) by using a non-integral O-ring or a ring-shaped gasket between a joint main body (pipe main body) and a pipe to be connected.
Further, a rigid synthetic resin is used for the joint main body; and a rubber or a flexible synthetic resin having an elasticity is used for the O-ring or the ring-shaped gasket, respectively.
However, since the O-ring is a flexible component which is smaller relative to the joint main body, and moreover, an attachment position is at an inner surface of the joint main body where the attaching is difficult, there has been a problem that an entanglement (twist) is generated in connecting with the pipe to be connected or in assembling the joint main body, causing leakage of a fluid or providing poor workability.
This invention provides a pipe made of a rigid thermoplastic resin in which a ring-shaped projection comprising an elastic resin and having a sealing property is integrally molded to an inner surface thereof thermoplastically.
In other words, this invention makes it possible to prevent generation of entanglement (twist) or leakage of a fluid and also makes it possible to improve the poorness of the operability accompanying the mounting, by integrally molding a pipe main body and a ring-shaped projection (which may be hereafter referred to as a ring-shaped projecting streak) streak having a sealing property along its inner surface directly (without intervention of a third component such as an adhesive) with a combination of a specific rigid thermoplastic resin and a specific elastic resin, respectively.
Now, the rigid thermoplastic resin to be used for the pipe (pipe main body) in the present invention may be, for example, a polyphenylene ether resin (a polyphenylene oxide resin), a polyamide resin, a polyester resin, a polyvinyl chloride resin, or an AS resin. Specifically, the polyester resin may be polybutylene terephthalate; the polyphenylene ether resin may be a mixture of polyphenylene ether and impact-resistant polystyrene; and the polyamide may be polyamide 46, polyamide 6, polyamide 66, polyamide 12, polyamide 612, polyamide 610 and the like, as preferable examples.
On the other hand, the elastic resin to be used for the ring-shaped projecting streak may be, for example, a butadiene-acrylonitrile rubber, a styrene-butadiene rubber, a nitrile rubber, a natural rubber, an ethylene propylene rubber, a chloroprene rubber, a fluorine rubber, a silicone rubber or a mixture thereof. Specifically, diene elastomers such as a butadiene rubber, a styrene-butadiene rubber, a chloroprene rubber, a butadiene-acrylonitrile rubber (a nitrile butadiene rubber) and the like, non-diene elastomers such as a isobutylene-isoprene copolymer, an ethylene-propylene, copolymer, chlorosulfonated polyethylene, chlorinated polyethylene and the like, thermoplastic elastomers such as a block copolymer of styrene and butadiene or isoprene, natural rubbers and the like are given as examples. These elastomers may be vulcanized and also may have a carboxyl group introduced by acrylic acid, methacrylic acid, sorbic acid or the like.
By combining the rigid thermoplastic resin and the elastic resin as mentioned above as materials for the pipe main body and the ring-shaped projection, the two can be integrally bonded thermoplastically. For details of further example materials and condition combinations, reference is made to each of Japanese Unexamined Patent Publication No. SHO 62(1987)-21244, Japanese Unexamined Patent Publication No. HEI 01(1989)-149854, Japanese Unexamined Patent Publication No. HEI 02(1990)-150439, Japanese Unexamined Patent Publication No. HEI 03(1991)-133631, Japanese Unexamined Patent Publication No. HEI 03(1991)-138144, Japanese Examined Patent Publication No. HEI 05(1993)-30182, Japanese Unexamined Patent Publication No. HEI 07(1995)-11013 and Japanese Examined Patent Publication No. HEI 08(1996)-18412.
In the present invention, the xe2x80x9csealing propertyxe2x80x9d for the ring-shaped projecting streak means that the sealing (seal) can be made by pressing contact with a tube to be connected, and is a property that can be obtained from use of the above-mentioned elastic resin by its physical property.
The pipe made of a rigid thermoplastic resin pertaining to the present invention can be manufactured by using materials and combinations as mentioned above by means of a manufacturing method such as follows.
In other words, the pipe made of a rigid thermoplastic resin pertaining to the present invention is manufactured by simultaneously or successively passing through a pipe main body molding step for molding a pipe main body and a ring-shaped projecting streak molding step for disposing a ring-shaped projecting streak on an inner surface of the pipe main body.
In the pipe main body molding step, the pipe main body is molded by injecting a molten material of the rigid thermoplastic resin (a source material of the rigid thermoplastic resin) into a tubular cavity (gap) formed by a set of molds which are splittable into a plurality.
Next, in the ring-shaped projecting streak molding step, the ring-shaped projecting streak made of the elastic resin and having the sealing property is integrally molded thermoplastically on an inner surface of the pipe main body by injecting a molten material of the elastic resin (concretely, an unvulcanized molten body as a source material or a material of a rubber) into a ring-shaped cavity formed a long the inner surface of the pipe main body by the molds themselves or combining another mold and vulcanizing it.
On the other hand, in the case where this ring-shaped projecting streak is to be molded simultaneously with the pipe main body, a manufacturing method of a pipe made of a rigid thermoplastic resin can be provided which comprises injecting, into a cavity formed by the splittable molds and comprising a pipe-shaped portion and a ring-shaped portion located along an inner surface of this pipe-shaped portion, a molten material of the rigid thermoplastic resin into the pipe-shaped portion and a molten material of the elastic resin into the ring-shaped portion of the cavity for simultaneous integral molding to obtain the pipe made of the rigid thermoplastic resin having the ring-shaped projecting streak on the inner surface of the pipe main body.
Here, if an injection inlet is formed in an inner mold of the molds, the material of the elastic resin in a molten state can be injected into the ring-shaped cavity located along the inner surface of the pipe main body. However, it is convenient if a through-hole is formed beforehand in a trunk portion of the pipe main body (using a slide pin) and the material of the elastic resin in a molten state is injected into the ring-shaped cavity using the through hole.
In the manner mentioned above, the ring-shaped projecting streak having a sealing property and made of an elastic resin is molded in a thermoplastically and integrally bonded state along the inner surface of the pipe main body made of the rigid thermoplastic resin by the pipe main body molding step and the ring-shaped projecting streak molding step.
The obtained pipe made of the rigid thermoplastic resin is convenient for connection of tubes and is especially suitable as a pipe joint that passes a pressurized gas containing air inside, water, oil or the like relative to the outside ambient air, because a sealing effect that does not allow passing of a gas such as air or liquid can be obtained when another tube is brought into close contact with the ring-shaped projecting streak having the sealing property, and a mounting operation of a separate O-ring or the like can be omitted.
Regarding the shape of the pipe joint, it can be applied to an L-shaped one (Elbow), a T-shaped one (T), a U-shaped one (U) or the like in addition to straight tubes in which the fundamental cross-section of the pipe is made into a circular shape, an elliptical shape, a square shape or the like.
Also, a connection structure of these pipe joints with a pipe to be connected, i.e. the pipe joint structure, may be concretely a pipe joint structure comprising a pipe main body composed of a rigid thermoplastic resin, a ring-shaped projecting streak made of an elastic resin and molded integrally along an inner surface of the pipe main body and having a sealing property, a release ring held at an opening of the pipe main body to be movable in an axial direction, and a locking spring which presses a trunk surface of the pipe to be connected that is inserted via the release ring to maintain a close contact state of the pipe to be connected and the ring-shaped projecting streak, and which deforms to release the pressing when the release ring is subjected to a moving operation inwards along the axial direction, thereby to enable insertion and detachment of the pipe to be connected. Here, these joint structures are not limited to simple pressing-in in the axial direction which is given as an embodiment, but may be a screwing (threaded engagement).
Also, the cross-sectional shape of the ring-shaped projection can be appropriately molded into a quadrangle, a trapezoid, a triangle, a semicircle, a U-shape, a V-shape or the like in a natural state depending on the relationship with the molding mold, the contact relationship with the pipe to be connected, the required extent of the sealing degree, and the like.
Concretely as a pipe joint structure, the present invention can provide a pipe joint structure comprising a pipe main body and a cap nut that is screwed to at least one opening of this pipe main body, in which a ring-shaped sealing portion (a ring-shaped projection or a projecting streak, the same applies hereafter) made of an elastic resin for sealing a pipe to be connected and/or the pipe main body is integrally formed on an inner surface (which may be hereafter referred to as inner circumferential surface of the pipe main body or the cap nut.
Here, specific example of the elastic resin as a material for the ring-shaped sealing portion and the resin made of the rigid thermoplastic resin as a material of an object portion of the pipe main body or the cap nut to which the ring-shaped sealing portion is integrally formed, are similar to those of the previously-mentioned case of the pipe made of a rigid thermoplastic resin, so that an explanation will be omitted.
According to another aspect, the present invention provides a pipe joint structure comprising a pipe main body and a connector inserted from one opening of the pipe main body, wherein the connector is formed of a rigid thermoplastic resin or a metal and includes a slip-off preventing protrusion on an outer circumferential surface of its insertion site; the pipe main body comprises a main body portion made of a rigid thermoplastic resin, an insertion mouth pipe portion made of a rigid thermoplastic resin which is molded separately from the main body portion and allowed to coaxially abut the main body portion to be integrally connected therewith, and a ring-shaped sealing portion made of an elastic resin which is integrally formed on an inner circumferential surface of the main body portion for sealing a tube to be connected that is inserted via the connector or the connector; and a recess groove is formed on an inner circumferential surface of an abutting portion of the main body portion and the insertion mouth pipe portion for engaging or engagingly stopping the slip-off preventing protrusion of the connector.
In other words, one of the constructional characteristics of the present invention is that a ring-shaped sealing portion made of an elastic resin is integrally formed on an inner circumferential surface of the main body portion made of the rigid thermoplastic resin, and also the main body portion and the insertion mouth pipe portion are coaxially abutted and integrally connected to form a recess groove on an inner circumferential surface of the abutting portion. Especially, it can be made into an inexpensive and high-sealing pipe joint structure by integrally forming the main body portion and the ring-shaped sealing portion with a combination of a specific rigid thermoplastic resin and a specific elastic resin, and by dividing the pipe main body along a plane that passes through the recess groove (the main body portion and the insertion mouth pipe portion) and molding them beforehand and then integrally connecting them.
In the present invention, the main body portion and the insertion mouth pipe portion are molded as separate bodies beforehand and then integrally connected concretely, they are integrally connected by integrally molding or winding a ring-shaped connecting portion (material) made of a rigid thermoplastic resin on an outer circumferential surface portion of an abutting portions of the two portions, welding or bonding the abutting portions of the two portions, or combining these.
In the present invention, the rigid thermoplastic resin and the metal to be used as the connector are not specifically limited. However, the rigid thermoplastic resin of the above-mentioned pipe main body and brass are given as preferable ones.
In the present invention, the slip-off preventing protrusion of the connector being engaged or engagingly stopped in the recess groove means that the slip-off protrusion fittingly falls into, is forcibly pressed into, or loosely enter the recess groove to stop at a wall of the recess groove.
According to another aspect, the present invention provides a manufacturing method of a pipe joint structure in which the pipe joint structure is obtained by molding each of a pipe main body and a connector, and inserting the molded connector into the molded pipe main body, wherein a step of molding the pipe main body comprises:
(1) a main body portion molding step for molding the main body portion by injecting a molten material of a rigid thermoplastic resin into a pipe-shaped cavity formed by splittable molds;
(2) a sealing portion forming step for integrally forming a ring-shaped sealing portion made of an elastic resin on an inner circumferential surface of the main body portion by injecting a molten material of the elastic resin into a small cavity formed on the inner circumferential surface of the main body portion by moving a part of an inner mold among the molds;
(3) an insertion mouth pipe portion molding step for molding an insertion mouth pipe portion by injecting a molten material of a rigid thermoplastic resin into a pipe-shaped cavity formed by other splittable molds; and
(4) a pipe main body forming step for forming the pipe main body in which the main body portion and the insertion mouth pipe portion are integrally connected, by coaxially and abuttingly disposing the molded insertion mouth portion and the molded main body portion and injecting a molten material of a rigid thermoplastic resin into a cavity formed by still another mold on an outer circumferential surface portion of the abutting portion to mold a ring-shaped connecting portion.
According to still another aspect, the present invention provides a manufacturing method of a pipe joint structure comprising integrally forming a ring-shaped rubber layer (a ring-shaped projection or projecting streak) thermoplastically on an inner circumferential surface of a pipe made of a rigid thermoplastic resin to obtain a pipe joint incorporating a sealing structure, by making an unvulcanized rubber (i.e., a clay-like source material or material of a rubber) into a ring-shape and performing vulcanization while allowing a close contact with the pipe made of the rigid thermoplastic resin.
In other words, in the present invention, by vulcanizing an unvulcanized ring-shaped rubber while keeping it in close contact with an inner circumferential surface of a pipe made of a rigid thermoplastic resin, since an unvulcanized rubber can be made into a viscous fluid by heating, the unvulcanized rubber can be vulcanized after it is brought into close contact and deformed in accordance with a shape of an inner surface of the pipe by utilizing its large deforming property and shape-retaining property. Therefore, the vulcanized rubber can be brought into close contact with the inner circumferential surface of the pipe in a free state instead of elastic deformation, so that a large sealing effect can be obtained, and it is made possible to provide a pipe joint having a high reliability in which leakage of a fluid caused by a weld, line of the pipe is not generated. Also, since the pipe made of a rigid thermoplastic resin and a ring-shaped rubber for sealing, which were separate components in the prior art, are integrally molded beforehand (before it is used as a pipe joint), the problems associated with aggravation of the assembling property and the operability by twisting or entanglement of the aforementioned ring-shaped rubber for sealing or the ring-shaped gasket can be eliminated.
Now, in the manufacturing method of the pipe joint pertaining to the present invention, the xe2x80x9cpipe jointxe2x80x9d as an object of manufacture means a joint for connecting two or more pipes (pipes to be connected), and the pipe joint incorporating a sealing structure means that a structure for connecting each pipe to be connected in a sealed state (close contact state) is provided in the inside.
Also, a pipe or a pipe main body (hereafter referred to as a pipe main body) is used as a main body of the pipe joint. As a material of the pipe main body, a rigid thermoplastic resin is given as an example. Specifically, a polyphenylene ether resin, a polyamide resin, a polyester resin, a polyvinyl chloride or an AS resin are given as preferable ones.
On the other hand, an unvulcanized natural rubber or synthetic rubber is used for integrally forming a ring-shaped rubber layer for sealing, on an inner circumferential surface of the pipe main body made of these rigid thermoplastic resins. Specifically, a rubber made of a natural rubber, a butadiene-acrylonitrile rubber, a styrene butadiene rubber, a nitrile rubber, an ethylene propylene rubber, a chloroprene rubber, a fluorine rubber, a silicone rubber or a mixture of these is suitably used.
Further, the above-mentioned ring-shaped unvulcanized rubber is disposed into a close contact state on an inner circumferential surface of the pipe main body made of the above-mentioned rigid thermoplastic resin and thereafter the ring-shaped unvulcanized rubber is vulcanized by adding a heat, whereby a ring-shaped rubber layer having a sealing property is integrally formed on the inner circumferential surface of the pipe main body. Here, in order to integrally form the pipe main body and the ring-shaped rubber layer without using an adhesive or the like, it is preferable to use a pipe main body made of a specific rigid thermoplastic resin and a ring-shaped unvulcanized rubber of a specific material property. As a combination thereof, the following combinations may be given as examples.
(1) A combination of a polyphenylene ether resin and an unvulcanized rubber comprising a styrene butadiene rubber (hereafter referred to as an SBR rubber), a natural rubber (hereafter referred to as an NR rubber), an ethylene propylene rubber (hereafter referred to as an EP rubber), or a nitrile rubber (hereafter referred to as an NBR rubber).
(2) A combination of a polyamide resin and an unvulcanized rubber comprising an NBR rubber, an EP rubber, a silicone rubber, or a fluorine rubber.
(3) A combination of a polyester resin and an EP rubber or a silicone rubber.
(4) A combination of an AS resin and an unvulcanized rubber comprising an NBR rubber.
(5) Further, a combination of a polyphenylene ether resin, a polyamide resin, a polyester resin, or an AS resin as above-mentioned, and an unvulcanized rubber comprising a mixture of an SBR rubber, an NBR rubber, an EP rubber, an NR rubber, a silicone rubber and a fluorine rubber and the like as mentioned above.
In the above combinations, the most suitable combination is selected in accordance with an intended usage of the pipe joint. Also, a paraffin or a naphthene oil as a flexibleening agent; a carbon black, a white carbon (silica) as a reinforcing agent; a stearic acid as an activating agent; a zinc white, N-cyclohexyl-2, BDMA, TAIC as a vulcanization promoting agent; a sulfur, a surface-treated sulfur, an organic peroxide, magnesium oxide, or a polyamine as a vulcanizing agent and the like are blended beforehand into the unvulcanized rubber, and its blending is suitably changed and selected in accordance with the intended usage.
Also, the unvulcanized rubber material is formed into a ring shape beforehand. The method for forming into the ring-shape may be, for example, a method of forming an unvulcanized rubber material into a thin plate shape and stamping out the plate-shaped unvulcanized rubber into a ring-shape; a method of slicing it after extruding it into a hollow tube shape; a method in which the rubber material extruded into an elongated strand shape is cut to a predetermined length and then winding it in a circular shape for forming; and the like.
The ring-shaped unvulcanized rubber thus formed can be made into a flexible clay form and has an extremely large deformability because it is unvulcanized in a literal sense of the word. This large deformability allows close adhesion in correspondence with the shape of the inner circumferential surface of the pipe main body. However, because of this large deformability, the rubber may conversely have a low shape-retainability. In such a case, an auxiliary method is necessary for allowing the rubber to be kept in close contact with a predetermined position on the inner circumferential surface of the pipe main body until the time of vulcanization (heating) while maintaining the shape of the ring-shaped unvulcanized rubber.
As this method, there may be mentioned, for example, a method in which, after a ring-shaped unvulcanized rubber is disposed at a ring-shaped rubber layer formation site of the inner circumferential surface of the pipe main body, a cylindrical body or a tubular body made of a metal having a diameter which is approximately equal to or a little larger than the inner diameter of the ring-shaped unvulcanized rubber is inserted and, with its circumferential surface, the ring-shaped unvulcanized rubber is pressed to be kept in close contact with the inner circumferential surface of the pipe main body; a method in which a ring-shaped step portion is formed at a ring-shaped rubber layer formation site in the inside of the pipe main body, a ring-shaped unvulcanized rubber is disposed at the step section, and thereafter a cylindrical body or a tubular body made of a metal having a diameter which is approximately equal to or a little larger than the outer diameter of the ring-shaped unvulcanized rubber is inserted from an opening of the pipe main body and, with its end, the ring-shaped unvulcanized rubber is pressed to be kept in close contact with the inner circumferential surface of the pipe main body; and further a method in which a ring-shaped groove is formed beforehand at a ring-shaped rubber layer formation site on the inner circumferential surface of the pipe main body, a ring-shaped unvulcanized rubber is disposed in the ring-shaped groove, thereafter a cylindrical body or a tubular body made of a metal and having a diameter which is approximately equal to or a little larger than the inner diameter of the ring-shaped unvulcanized rubber is inserted and, with its circumferential surface, the ring-shaped unvulcanized rubber is pressed to be kept in close contact with the ring-shaped groove of the pipe main body.
Also, there may be mentioned, for example, a method in which a ring-shaped groove is formed on the inner circumferential surface of the pipe main body, a plurality of holes leading to an outer surface of the pipe main body from the bottom surface of the groove are formed approximately with equal angular spacing, a ring-shaped unvulcanized rubber is disposed in the groove, and thereafter suction is performed from the holes on the outside surface of the pipe to allow the ring-shaped unvulcanized rubber to be in close contact with the inner circumferential surface of the pipe main body; a method in which a heat-resistant rubber balloon is inflated in the inside of the pipe main body and a ring-shaped unvulcanized rubber is allowed to be kept in close contact with the inner circumferential surface of the pipe main body by a pressing force of the balloon.
Next, as a method for vulcanizing the ring-shaped unvulcanized rubber disposed and brought into close contact as mentioned above at a predetermined position of the inner surface of the pipe main body, there may be mentioned, for example, a method in which a cylindrical body or a tubular body made of a metal (for example, made of aluminum or copper) inserted for allowing the ring-shaped unvulcanized rubber to be in close contact with the inner circumferential surface of the pipe main body is heated to a predetermined temperature to transfer heat to the ring-shaped unvulcanized rubber via the cylindrical body or the tubular body for heating; a method in which the pipe main body having a cylindrical body or a tubular body made of a metal inserted into the ring of the unvulcanized rubber is heated as a whole in a high temperature tank of a predetermined temperature; and a method in which a cylindrical body or a tubular body made of a metal or made of a synthetic resin is inserted into the ring of the unvulcanized rubber to allow the unvulcanized rubber to be in close contact with the inner circumferential surface of the pipe main body and then, after the cylindrical body or the tubular body is drawn out, the remaining unvulcanized rubber and the pipe main body are heated in a high temperature tank.
By heating of the unvulcanized rubber by these methods, an additive agent, a vulcanizing agent, a vulcanization promoting agent, and a vulcanization promoting auxiliary agent and the like which have been kneaded beforehand into the unvulcanized rubber react with the rubber, whereby a ring-shaped rubber layer is formed which has a property suitable as a ring-shaped rubber layer having a sealing property and which is fixed in close contact with the inner circumferential surface of the main body to be integral with the main body.